1. Field of Invention
The present invention relates to a sound-reducing device for insertion inside a pneumatic tire.
2. Background
The radiation of sound from a motor vehicle tire, in addition to wind and engine noises, contributes to the overall sound emission of a motor vehicle to a relatively great extent. One of the causes of this is the running noise that comes from the impact of tire""s running surface on the surface of the roadway. The configuration of the tire profile has a significant influence on this. In this connection, several measures are already known to reduce tire noise by changing the pitch cycles of the tire""s running surface. These changes bring about a redistribution of the vibrations of the tire into a broader frequency band. This, in turn, reduces the so-called vibration xe2x80x9cpeaksxe2x80x9d in the audible range and hence a reduction in audible noise. As in the case of noise-reducing rubber mixtures, the difficulties which have resulted from this approach lie in the particular influence which the running strip profile has on the driving characteristics of the motor vehicle.
Further developments involve absorbing the noise that arises upon the movement or the rolling of the tires, to the greatest extent possible, within the immediate vicinity of the area of its origination, such as by placing sound-absorbing devices in the wheel casing of the motor vehicle, for example. Here, too, the additional expense and the changes in the body of the vehicle are to be noted as disadvantages.
One additional cause of noise lies in the vibrations of the running strip and of the side walls of a rotating motor vehicle tire which, upon leaving the standing surface of the wheel, oscillate in their natural oscillational forms. The natural oscillational forms of the belt are also more noticeable here. Here, measures for the reinforcement of the side walls or for the connection of both side walls within the pneumatic tire by means of support braces are already known in this connection.
All of these vibrations are transmitted to the air column within the interior of the tire which, in turn, passes them on to a not-insignificant extent. Moreover, through formation of stationary waves and the reaching of certain natural oscillation frequencies, these vibrations can be amplified even more and fed back into the components of the tire.
The placement of foam material rings in the torus space, or even the filling out of the torus space with sound-absorbing material is likewise known. See German Patent No. DE 43 25 470 A1, for example. This approach not only makes mounting of the tires more difficult, but also increases overall weight. Moreover, because of the non-uniform way in which the torus space may be filled, considerable problems are encountered regarding balancing of the wheels at high speeds.
German Patent No. DE 41 20 878 C2, on the other hand, describes a motor vehicle tire in which reinforcements are connected to opposing side walls on the interior of the tire in a force locking manner. In particular, these reinforcements are vulcanized to the inner sides of the tire side walls by way of ring-shaped bands. By means of this arrangement, the vibrations of the side walls as well as the transmission of these vibrations to the air column in the interior of the tire are damped. These reinforcements, which are uniform in terms of radial shape as well as placement along the circumference of the tire are capable of vibration and act in a damping manner. However, they also form natural vibrations. In addition, only the vibrations of the side wall are influenced, but not the vibrations of the running strip and of the belt.
U.S. Pat. No. 5,479,974 presents a noise-reducing system for tires with flexible, non-self-supporting flaps attached to the rim, which are preferably made from textile materials which are moved, by means of centrifugal force, in the radial direction and subdivide the interior of the tire into several chambers. By this means, vibrations in the interior of the tire should also be damped, and a change of the wavelength or of the amplitude during the stationary waves of the air column which are formed should be brought about.
The provision of the large-surface flaps, which are not stable, particularly at lower driving speeds, as well as the possibility of a xe2x80x9cflutteringxe2x80x9d or xe2x80x9cstrikingxe2x80x9d or a vibration of the body into transitional speeds between a stable and an unstable position, which directly leads, through the relatively great mass of the individual elements (flaps), to the bringing about of additional noises, is disadvantageous in this arrangement.
The task of the invention has thus been that of absorbing the vibrations of the air column located in all of the tires, in all conditions of driving, but without creating, through the assembly units, an additional strongly vibrating system, and without influencing the driving characteristics and the construction of the tire component or the body of the vehicle in an unfavorable manner.
The sound absorber of the present invention is comprised of a web or system of flexible fibers which is connected with a strip-shaped support fabric, in which the support fabric is attached, with its internal side turned away from the web, to the external side of the bead of the rim, and the fibers of the web extend, inside the hollow space which is formed between the rim and the tire in the radial direction.
Such a sound-absorbing assembly has a very slight mass or a slight weight, as the result of which the centrifugal forces which are brought about are kept very low, even at a high rotational speed of the wheel, and no markedly increased stressing of construction parts, such as bearings, wheel supports, stabilizers, etc., is brought about. Through the flexible development of the fibers, in addition, a problem-free mounting of the tire on the rim is possible, since the tire bead simply slides over the fibers, and can be displaced to the opposite rim seat.
Furthermore, such a sound-absorbing assembly, consisting of fibers extending radially inside the hollow space which is formed between the rim and the tire, has an extraordinarily high absorption capacity over a very wide frequency band. In this, the particularly high-intensity components of a sound field are absorbed independently of the frequency. The individual fibers, which are positioned densely against one another and extend in a radial direction, thereby form an absorption body which not only acts in a strong damping manner, but also impedes, to the greatest extent possible, the formation of stationary waves.
The width of the support fabric strip of the inventive absorber can be formed in any manner desired and thus, for example, also extends over the entire free width of the rim between the tire beads, although it preferably occupies only a fraction of the width of the rim, however, since a simpler mounting is made possible by that means.
One particularly advantageous development of the sound-absorbing assembly consists of the fact that the fibers of the web are formed as non-self-supporting fiber which, upon the rotation of the motor vehicle wheel, are moved in the radial direction under the influence of the centrifugal force inside the hollow space that is formed between the rim and the tire.
Through such a development, the mounting is not only first of all simplified, since the non-self-supporting fibers are applied to the rim without the influence of centrifugal force or under the influence of gravity, and thereby occupy a position of equilibrium, and are not, for example, set against any kind of resistance to a tire to be drawn onto the rim, which tire is, in point of fact, moved with its tire beads through the drop base. In addition, any materials can be used for fibers in such an implementation, particularly such as are formed to be particularly soft or elastic and, for this reason, have increased absorption characteristics if they are brought under the influence of centrifugal force.
One additional advantageous development consists of the fact that fibers of the web and/or the fibers of the support fabric consist of several individual filaments, or bundles of filaments, which are interwoven or stranded with one another, if necessary.
In this, the filaments of the web fibers are, in particular, interwoven or stranded in a loose bond, in such a manner that the individual filaments do not touch one another over the entire length of the fiber, as the result of which openings or hollow spaces arise within the stranded or interwoven material and the filament bond which forms the specific fiber, through which the ability to absorb is further increased. One further effect which results from this is that these openings or hollow spaces are closed again when the centrifugal force becomes stronger, as the result of which an adjustment of the absorption capacity is made possible in dependence on the rotational speed of the wheel.
In this manner, the fibers of the web cannot only be adjusted in their elasticity, but can also be formed from individual filaments of different materials with adjusted absorption/damping characteristics. This advantage also results for the support fabric, whereby the strength or the extensibility of the support fabric can also be further adjusted.
One further advantageous development consists of the fact that the individual fibers and/or filaments of the web are formed, at least in part, as spatially-formed fibers or filaments, particularly as fibers or filaments formed in a undulating or helical manner. The noise absorption capacity of the web is, first of all, further increased through such a development. This is brought about through material fibers which are longer overall resulting in more damping material made available through the spatial deformation. Such a construction also provides an increased and more strongly diffused reflection of the sound waves by such an undulating or helical twisting or torsion, through which the development of stationary waves is made still more difficult.
These effects can be amplified still further through an additional advantageous development in which the individual fibers of the web are interwoven or interlaced with one another in a loose connection.
The fibers of the web and/or the fibers of the support fabric are, in an advantageous manner, formed as synthetic fibers, preferably as polyamide, polyester, polyvinyl-alcohol (PVA), aramide, carbon, or glass fibers. Through the use of such materials, as well as through the use of mixed materials, if necessary, an influence can be brought about on the absorption ability of the sound-absorbing assembly, depending on the design. The use of hollow fibers is thereby also advantageous in regard to the absorption capacity.
In one additional advantageous development, the support fabric is formed as a closed annular strip, whereby the fibers of the support fabric consist, at least partially, of a shrinkable material. The sound-absorbing assembly can thereby be produced as a pre-manufactured ring with such an excess dimension that it can easily be slid over the horns of the rim, and can thereupon be fixed to the rim in its end position by means of a shrinking process, such as by means of water-shrinkable or heat-shrinkable threads or filaments, for example, through which an adhesion or further fixing can be dispensed with.
The support fabric can, of course, also be glued on its internal side to the radial external side of the rim, whereby an overlapping area freed from the web is preferably provided in order to connect the ends of the support fabric strip. The support fabric strip can, during the formation of such an overlapping area, and specifically depending on the centrifugal forces or rotational speeds which are to be expected, likewise be tightened around the radial external side of the rim, whereby only the ends of the support fabric are then glued to one another.
One further possibility consists of creating the support fabric strip in the form of closed, ring-shaped strips, whereby the support fabric material has elasticity such that it can be additionally lifted over the horns of the rim relatively easily, and then elastically tightened onto the rim by means of resilience.
The support fabric is advantageously coated, at least on its internal side, with sound-damping material, preferably with layers of foam or rubber. By this means, a damping of the vibrations of the body of the rim is brought about, in addition to the absorption of noise through the web fibers within the torus space. This results in making the transmission of vibrations within the torus space even more difficult.
Both the web fibers, as well as the fibers of the support fabric, can thereby be formed as fibers with a high modulus of elasticity and high temperature resistance. These fibers provide high damping capability, a secured fixing to the rim and secure sound absorption, even upon the heating of the tire or the parts of the tire or of the torus space.
One additional advantageous development consists of the fact that the support fabric is connected with the tire bead, on at least one side, in the area of the bead profile or in the area of the rim seat. By means of such a development, the tire and the support fabric with its web can be mounted to the rim in one work process, whereby the use of shrinkable fibers for the support fabric is appropriate in the event of a connection to one side only, through which a one-sided clamping in the area of the bead and a shrinking down of the remaining width of the support fabric strip are carried out on the radial external side of the rim. In the event of a two-sided connection, the support fabric strip covers over the entire width of the rim and is clamped to both sides, in the area of the rim seat, by the tire bead, whereby the use of shrinkable fibers for the support fabric is appropriate for a shrinking down over the entire width of the rim here as well.
One additional advantageous development consists of the fact that the web fibers are formed in different lengths over individual areas of circumference of the rim. If, for example, areas of the sound-absorbing assembly, with web fibers longer in relation to the remaining areas, are symmetrically distributed at angular distances over the circumference of the rim of 60xc2x0 or 30xc2x0, then the absorption capacity is further increased in relation to the circumferential sound waves which are brought about within the torus space.